BANGKOK (Reuters) - The world's hottest region for mobile video games, Southeast Asia, may be set to cool off amid early signs of the curse of makers of titles like "Minecraft" and "Candy Crush Saga" - the prospect of market saturation after a wave of smartphone buying.

Games revenue in Thailand, its leading light, is set to grow 50 percent a year to $485 million in 2018, according to market research firm Newzoo, helped by new 4G mobile spectrum that boosts Internet speed. But revenue, stoked by purchases of in-game virtual accessories, surged 86 percent last year.

For Southeast Asia, Newzoo expects revenue to grow about 40 percent a year to $2.25 billion by 2018, down from nearly 60 percent last year. Growth is still easily outpacing more saturated China, Japan and South Korea for game makers like Microsoft's Mojang and King Digital Entertainment Pcl, but industry insiders say all eyes are now on what happens next in Thailand, the region's biggest market.

"Thailand is becoming a key market for mobile games and studios," said Jakob Lykkegaard, co-founder and Chief Executive Officer of Hong Kong-based Playlab, developer of the game "Juice Cubes".

The country's surge to gaming prominence has come as Naver Corp's Line messaging service estimates Thais spend on average 5.7 hours per day on smartphones. Soon, however, the focus may switch to Indonesia, likely to become the region's number one in 2018 due to its huge population, a growing middle class and rising mobile internet penetration, Newzoo says.